The present invention relates to the technical background of tank venting in internal combustion engines with gasoline direct injection.
Engines having gasoline direct injection may be operated in both stratified mode and homogeneous mode.
An engine control program that controls switching between the two modes of operation is described in German Published Patent Application No. 198 50 586.
In stratified mode, the engine is operated with a highly stratified cylinder charge and a very lean mixture to minimize fuel consumption. The stratified charge is achieved by late fuel injection, which divides the combustion chamber into two zones: The first zone contains a combustible air/fuel mixture cloud near the spark plug. It is surrounded by the second zone, which includes an insulating layer of air and residual gas. The potential for optimizing consumption derives from the ability to operate the engine largely unthrottled, thus avoiding charge cycle losses. Stratified operation may be performed when loads are comparatively low.
At higher loads, when performance optimization is important, the engine is operated using a homogeneous cylinder charge. This homogeneous cylinder charge results from early fuel injection during intake. This results in a longer interval between combustion and mixture formation. The potential of this mode to optimize performance derives, for example, from its ability to utilize the entire combustion chamber volume for filling with combustible mixture.
Varying amounts of fuel vapor per time unit exist in the fuel tank of a vehicle, depending on fuel temperature, fuel type and pressure ratios. A method is conventional known for first storing this fuel vapor in an active charcoal filter and then supplying it, mixed with air, to the engine combustion system via a controllable tank venting valve during operation of the internal combustion engine. The active charcoal filter thus becomes able again to absorb additional fuel vapor (regeneration). The fuel vapor that has been mixed with air is referred to as regeneration gas.
To compensate for the amount of fuel flowing via the tank venting valve, the amount of fuel flowing via the injectors is reduced. In this connection, a method for obtaining a measure FTEAD of the fuel content of the regeneration gas from known quantities in the control unit, including the fuel flow via the injectors, the quantity of regeneration gas when the tank venting valve is open, the intake air quantity of the engine and the signal of an exhaust gas analyzer probe, is described in German Published Patent Application No. 38 13 220 for engines with intake-manifold injection. The obtained measure serves to adjust the reduction in fuel flow via the injectors with the fuel flow via the tank venting valve, with the goal of controlling the composition of the entire air/fuel mixture. During operation of an engine with intake-manifold injection, the combustion chamber is homogeneously filled with mixture, just like during operation of an engine with gasoline direct injection in homogeneous mode. It is therefore possible to use tank venting control in this mode, as is conventional from the field of intake-manifold injection.
During operation of an engine with gasoline direct injection in stratified mode, on the other hand, disturbances tend to occur when controlling the entire air/fuel mixture with an open tank venting valve.
It is an object of the present invention to eliminate such disturbances and thus improve predictability of the effect of tank venting on the mixture composition in stratified mode.
Specifically, the determination according to the present invention of the fuel content of a regeneration gas during regeneration of an intermediate fuel vapor storage unit in internal combustion engines having gasoline direct injection in lean (stratified) mode, in which the stored fuel vapor is supplied to the internal combustion engine in the form of regeneration gas via a controllable tank venting valve, and in which the signal of an exhaust gas analyzer probe in the exhaust gas of the internal combustion engine is taken into account to determine the fuel content, includes the following steps:
Adjustment between the exhaust gas analyzer probe signal and a preselected setpoint when the tank venting valve is closed, with the exhaust gas analyzer probe signal being combined with a correction quantity when the tank venting valve is closed so that the result of the combination corresponds to the setpoint.
Combination of the exhaust gas analyzer probe signal in the same manner with the correction value obtained earlier while the tank venting valve is open; and
Determination of the regeneration gas charge based on the result of the combination.
The present invention is based on the concept that, in stratified mode, the measured lambda value may vary to a comparatively large degree from the physical lambda value.
Possible causes include probe manufacturing tolerances, aging effects and greatly fluctuating exhaust gas temperatures in stratified mode with unregulated probe heating. Regardless of the cause at hand, a deviation nevertheless occurs between the probe signal and the actual lambda value.
It is an object of the present invention to adjust the probe signal in stratified mode with the tank venting valve closed. This decouples the probe signal from the absolute lambda value. If the regeneration gas additionally has an effect when the tank venting valve is open, this effect may be determined from the relative change in the probe signal.
According to one example embodiment of the present invention, a measured lambda value (measured lambda) is formed from the exhaust gas analyzer probe signal, and the difference of the measured lambda value is determined from the product of the adjustment factor and the difference of the lambda setpoint (setpoint lambda) from value 1 and integrated.
According to another example embodiment, the adjustment factor in the steady state corresponds to the average quotient
(measured lambdaxe2x88x921)/(setpoint lambdaxe2x88x921).
With this function, fluctuations in the measured lambda are averaged out through the integration process during adjustment, thus preventing corruption of the adjustment factor.
According to a further example embodiment, the actual lambda is determined by the following equation during operation with an open tank venting valve:
Actual lambda=(1/adjustment factor)*(measured lambdaxe2x88x921)+1
According to a further example embodiment, a new adjustment is performed in stratified mode upon a change in the operating point of the internal combustion engine or when certain ambient conditions change.
According to a further example embodiment, the ambient temperature and the altitude at which the engine is operated are ambient conditions of this type.
According to a further example embodiment, a change in the operating point is defined by a minimum change in the lambda setpoint.
According to a further example embodiment, an adjustment ends when the absolute value of the integrator input drops below a predetermined threshold value.
The present invention also relates to an electronic control unit for performing at least one of the methods and example embodiments described above.
One example embodiment of the present invention is explained below on the basis of the drawings.